This is a transcription by Helmut Bornefeld of "Gesang der Geharnischten" (Song of the armoured men) from the Magic Flute - in fact a chorale prelude. This rendition is rather traditional. A 4' reed would have been nice, but there is none on the Trost.
For a recording closer to Bornefeld's ideas on registration, listen to my next post on the Marcussen set.
Mozart's accompanying subject is very close to a little fugue by Pachelbel - just turned from c major to c minor. I have posted this fugue as well - just for curiosity.